and apart from me screwing it up and now its loud but still works

pirvan wrote:

Ball screws are more efficient that lead screws as they have less friction.  The lower friction coefficient, means they can be driven faster without wear and tear, and impose a smaller load on the motor (require less torque).

Agreed. Note that MC's leadscrew came with a stepper motor permanently attached to it too - that was one of the attractions, and probably brings the price up a bit...

No doubt it would be beautiful, but I would think that for the SD z-axis a ballscrew is way overkill. They're indispensable if you need to apply a bit of force with the axis (e.g. cutting machines) and still want no backlash, but the backlash nut will be more than capable in this case. As long as the motor can handle it, a bit of friction won't be a killer here either - esp. as the z-axis can be pretty slow and it doesn't matter too much.

The trapezoidal thread may be made more accurately than the usual M3/M5 threaded rods that are used commonly as a z-axis upgrade - I can see this being pretty slick! Looking forward to seeing some smooth prints.

It's still an issue of cost. 

I agree that buying a ballscrew from one of the major hardware places like McMaster Carr would cost a small fortune, but there are a lot of cheaper alternatives.

There are many Chinese vendors on eBay selling them for cheap.  I bought a SFU1204 x 350mm screw for like $40 shipped, then got a 8mm x 5mm flex adapter for another $5-6.

My conversion to a ball screw cost less than $50.00 in parts, and installation on the aluminum bed takes about 15 minutes.

http://www.soliforum.com/post/42550/#p42550

adrian wrote:

getting the torque back

Full step torque is constant wrt micro stepping. By extension, increased micro stepping resolution does not change the holding torque at multiples of the original micro stepping resolution.

1/32 = some fraction of 1/16 holding torque
2/32 = same as 1/16 holding torque
3/32 = some duration of 1/16 holding torque
4/32 = same as 1/16 holding torque

etc...

was in reference to torque of movement at 1/4 vs 1/16 vs 1/32 etc, where there is a degradation of the torque applied relative to the torque that can be applied as a full step..... not that its different within bands of steps within the same steps

anyway - wrt to the whole steps things in the specific instance - I never looked at the specs and just took molecular concepts word for it being 8*2 so my apologies for the bum steer there but at least that got sorted out 

Ball screws are more efficient that lead screws as they have less friction.  The lower friction coefficient, means they can be driven faster without wear and tear, and impose a smaller load on the motor (require less torque).

Agreed. Note that MC's leadscrew came with a stepper motor permanently attached to it too - that was one of the attractions, and probably brings the price up a bit...

No doubt it would be beautiful, but I would think that for the SD z-axis a ballscrew is way overkill. They're indispensable if you need to apply a bit of force with the axis (e.g. cutting machines) and still want no backlash, but the backlash nut will be more than capable in this case. As long as the motor can handle it, a bit of friction won't be a killer here either - esp. as the z-axis can be pretty slow and it doesn't matter too much.

The trapezoidal thread may be made more accurately than the usual M3/M5 threaded rods that are used commonly as a z-axis upgrade - I can see this being pretty slick! Looking forward to seeing some smooth prints.

getting the torque back

Full step torque is constant wrt micro stepping. By extension, increased micro stepping resolution does not change the holding torque at multiples of the original micro stepping resolution.

1/32 = some fraction of 1/16 holding torque
2/32 = same as 1/16 holding torque
3/32 = some duration of 1/16 holding torque
4/32 = same as 1/16 holding torque

etc...

spent the last of my money on the leadscrew, i almost never need a drill the dremel will usually suffice . whatt i need is to borrow a drill lol

heres the link if anyone is interested, it isnt very exspensive  $75 total (shipping was $28 or close to it) and its just about the right length  I dont think Im going have to cut it down.

http://www.robotdigg.com/product/8/Thre … -Leadscrew

Im kinda sick today but when I around to installing it Ill post some pictures and let ya know how it went

I just started to read this post, and at over $100 shipped that sounds like a hell of a lot of money for a lead screw.  Why not get a ball screw for that kind of money?

Ball screws are more efficient that lead screws as they have less friction.  The lower friction coefficient, means they can be driven faster without wear and tear, and impose a smaller load on the motor (require less torque).

MolecularConcept wrote:

i have my jumpers set to 1/4 step but the steps per/min that actually work are for whole steps... right now its at 100.

Pitch is the space between teeth (which you've measured to be 2mm).
Lead is the amount the nut moves down the rod per rotation (which, given it's a T8x8 is 8mm).

T8x8(P2):
* T8 is an 8mm diameter trapezoidal thread
* x8 means 8mm LEAD
* (P2) means 2mm PITCH (which indicates it must be 4-start, as 4x2=8)

Look at the end of the rod and count the number of tooth ends... There should be four!

200 steps/rev x 4x microstep (pulses/step) = 800 pulses/rev
800 pulses/rev / 8 mm/rev = 100 pulses/mm (as you have set currently)

Edit: also confirmed by the backlash nut specs: http://www.robotdigg.com/product/18/Ant … -Leadscrew

+1

i have my jumpers set to 1/4 step but the steps per/min that actually work are for whole steps... right now its at 100.

Pitch is the space between teeth (which you've measured to be 2mm).
Lead is the amount the nut moves down the rod per rotation (which, given it's a T8x8 is 8mm).

T8x8(P2):
* T8 is an 8mm diameter trapezoidal thread
* x8 means 8mm LEAD
* (P2) means 2mm PITCH (which indicates it must be 4-start, as 4x2=8)

Look at the end of the rod and count the number of tooth ends... There should be four!

200 steps/rev x 4x microstep (pulses/step) = 800 pulses/rev
800 pulses/rev / 8 mm/rev = 100 pulses/mm (as you have set currently)

Edit: also confirmed by the backlash nut specs: http://www.robotdigg.com/product/18/Ant … -Leadscrew

today i had an idead to switch the components around basically used the solidoodle motor coils and the chineese bearing holders(silver parts) and the ACME rotor. it works it was nice and quiet  till i mounted it to the case. thinking of some kind of rubber gasket to isolate some of the sound? i dunno what to use though.

anyway its still loud but it spins. i have my jumpers set to 1/4 step but the steps per/min that actually work are for whole steps i dunno what the hell is going on.  right now its at 100. and im calibrating it as im writing this.

the Z wobble is completely gone i have no more ribbing on the sides and front. and the only thing that i need to work on is the anti backlash nut needs dremeled a tiny bit cause it hits the y jackshaft when its in the home position

So yeah, it appears to be a 4 start 8mm pitch screw, which would have been nice to verify with a caliper before trying to do the math ahead of time. Obvious robotdigg is wrong about a 2mm pitch.

... cause it kinda rattled around

Drill chatter when starting the hole is exactly what the center punch helps eliminate. . And it most likely (unless if your smaller bit was really blunt?) would have been worse if you started with a larger diameter drill bit. Glad it worked, just FYI if you do this again.

W/o punch applying firm pressure and starting really slow is even more important, to the point it might be bad for your bit (since you're initially using it to "scrape" the surface at slow speed) -- at least in my experience, feel free to correct me. A fresh, sharp bit also always helps.

Edit: Here, this explains whys better than me http://en.wikipedia.org/wiki/Pilot_hole (note explanation about bit chisel, and remark about punch)

8mm travel / rev (specs)
200 full steps / rev (specs)
16 (micro)steps / full step (my guess)

Doing math, keeping dimensions (as in physics term) to illustrate (sanity check: full steps and revs cancel out):

(16 steps / full step) * (200 full steps / rev) / (8 mm / rev) = 400 steps / mm

This is all the calculator does, you get idea... Just substitute your numbers (if you have a DRV and haven't changed jumpers, Adrian is right, it's 32 micro steps / full step, so answer is 800).